What is a Glycemic Index?

The glycemic index, is a measure of the effects of carbohydrates on blood sugar levels. Carbohydrates (carbs for short) that break down quickly during digestion, release glucose rapidly into the bloodstream, have a high GI; carbs that break down more slowly, release glucose gradually into the bloodstream, have a low GI.

The GI concept was developed in 1980 at the University of Toronto in a study to determine which foods were best for people with diabetes. A lower glycemic response (below 55) usually equates to a lower insulin demand and may improve long-term blood glucose control and blood lipids compared to medium (56-69), or high (greater than 70).

The quantity of fiber, whether it is liquid or solid, and preparation or cooking methods affects the GI value of a meal. Generally speaking, however, highly processed foods with a lot of refined sugars will also have a higher GI. The GI for any food may also notably differ among individuals.

Differences or Similarities Between the Low Carbohydrate Diet and the Low GI Diet

The premise behind low carbohydrate (carb for short) diets is that all through the day blood sugar, and therefore, insulin levels, are so low that the body is forced to use fat as its main source of fuel. This is similar to what occurs with low GI diet plans. However, the difference lies in low GI diets not restricting carbohydrate intake. Low GI diets are just very discriminating of the carbs picked for consumption.

What is a Glycemic Load?

The glycemic load is a ranking of how much a standard serving of food raises ones blood sugar. The glycemic load of a particular food is calculated by multiplying the amount (in grams) of carbohydrate in a serving by the glycemic index and dividing that number by 100. For example, the glycemic load of a pear with a GI of 25 and 21 grams of carbs is GL = 25 x 21g divided by 100 = 5. The GL of a 2.4 ounce French fries with a GI of 54 and 21 g of carbs is GL = 54 x 21g divided by 100 = 11. The fries have more than 2x the glycemic effect of a pear.

Five Myths Akin to the GI.

Myth 1 — Potatoes and other white carbs should be avoided because they contain high GI values.

Color of food does not fundamentally determine a high GI. As referred to above, preparation method, quantity of processing and meal composition influence GI, not food color. For instance, the white bread consumed with 35 grams of olive oil has less GI (20) than white bread consumed with 35 grams butter (78). In this example, eating pasta or white bread in combination with fat and protein at mealtime changes their overall GI values.

Myth 2 — The quantity of carbs and sugar in certain foods is established by its GI value.

GI declares nothing on carb content. It simply describes the rate glucose is released in the bloodstream. Look at the GL examples above. Both pear and fries have equal number of grams of carb but the fries have a higher GL value. On the other hand, one could consume two unlike foods with a comparable GI. The blood glucose response will still be larger for the food eaten in higher quantity.

Myth 3 — Simple sugars are all high in GI.

The GI for most raw fruit is between 30-50 even though they contain the simple sugar fructose (GI 21). Most fruit have a slower rate of absorption and digestion than glucose (GI 93) another simple sugar.

Myth 4 — GI values can prejudge healthy versus unhealthy foods.

The GI does not point to whether a food is healthy or not. For example, whole milk has a GI of 27 whereas skim milk has a GI of 32. In this example, lower GI doesn’t constantly mean a healthier product because whole milk contains saturated fat making it a less than healthier choice.

Myth 5 — I can eat as much low GI food as I want and sustain low insulin levels.

Keep in mind that the glycemic response is a fusion of GI and carb density. Hence, higher carb consumption will still payoff in higher insulin levels even with low GI values.

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